Alcohol abuse, however defined, is a major health problem for Western societies. In the U.S., alcoholism has become the fourth most common cause of death in adults. Not all who abuse alcohol develop liver damage (estimates range from 10 to 31%); however, the standard mortality for cirrhosis (95% due to alcoholic liver disease) is greater than 90/100,000 for professional and technical workers. Steady drinkers are more at risk for cirrhosis than are intermittent drinkers; this suggests that intermitent ingestion allows the liver time for repair. In any case, the regenerative ability of the liver is crucial to its recovery from alcohol-induced disease. The proposed research will investigate the molecular mechanisms controlling normal and alcohol-damaged liver regeneration. Cell division is virtually nonexistent in normal mammalian liver. However, following chemical, viral or physical damage, the liver responds by initiating DNA synthesis and mitosis, which results in restoration of organ mass. This response is synchronous and is thought to be controlled by modulators of DNA synthesis. This regenerative process is known to be defective both in vivo and in vitro after administration of ethanol. In spite of intensive investigation, the molecular mechanisms controlling proliferative homeostasis in the liver remain unknown. Recently we have developed a biological assay to detect mRNA species which code for modulators of DNA synthesis. We have employed this microinjection technique to identify both an inhibitory fraction in resting rat liver mRNA and stimulatory fractions in regenerating rat liver mRNA. mRNA species from resting rat liver which code for inhibition have been enriched and a cDNA library has been generated. The project proposed here is to isolate cDNA clones complementary to both inhibitors and stimulators of DNA synthesis transcribed in rat liver. Study of the inhibitor(s) may give insights into the development of hepatocarcinoma since loss of a DNA synthesis inhibitor might lead to immortalization. Study of the expression of the stimulators during normal regeneration will provide a comparative standard which should help in identifying the ethanol-sensitive pathways involved in defective liver regeneration. Further, knowledge of the mechanisms for initiation of regeneration point toward future therapies based on in situ regeneration of alcohol-damaged liver tissue.